1. Field of the Invention
An aspect of the invention relates to an Internet Protocol (IP) address allocation, and more particularly to a method of obtaining IP address allocation information of a neighboring network in a mobile node to enable the mobile node to receive a new IP address when it moves to the neighboring network.
2. Description of the Related Art
A rapid increase in users of mobile communication services has led to activation of mobile communication services supporting multimedia communications, and seamless communication services have been requested by mobile users. Accordingly, it has become important to achieve a fast handover in a wireless local area network (LAN) environment based on the IEEE 802.11 specification.
FIG. 1 illustrates a wireless LAN environment in the related art.
Referring to FIG. 1, the wireless LAN environment includes a mobile node (MN) 1, an access point (AP) A 10, an access point B 20, an access point C 30, an access point D 40, an access router (AR) A 50 and an access router B 60.
The mobile node 1, which can be a mobile phone, a personal digital assistant (PDA), a notebook computer or any other wireless device capable of accessing a wireless LAN, moves between several wireless LANs. Each of the access points A, B, C and D 10, 20, 30 and 40 connects the mobile node 1 to a subnet to which the mobile node 1 belongs, thereby allowing the mobile node 1 to access a wired network like the Internet. Hereinafter, a device performing this role will be called an “access point.”
The access routers A and B 50 and 60 provide the mobile node 1 with routing services in a subnet to which each of them belongs, thereby allowing the mobile node 1 to access an arbitrary node in the subnet using an optimal path.
As illustrated in FIG. 1, the wireless LAN environment in the related art will be described under the assumption that the mobile node 1 passes through a basic service set (BSS) managed by the access point A 10, a BSS managed by the access point B 20, a BSS managed by the access point C 30 and a BSS managed by the access point D 40 in sequence. BSS is a term used in the IEEE 802.11 specification, and it refers to a wireless LAN managed by a single access point.
In order to allow the moving mobile node 1 to know which access point to use for accessing a wired network, each of the access points A, B, C and D 10, 20, 30 and 40 periodically transmits a beacon signal that indicates its managed BSS.
In a communication denoted by 11 in FIG. 1, the mobile node 1, which has been positioned in the BSS managed by the access point A 10, receives a beacon signal from the access point A 10. Based on the received beacon signal, the mobile node 1 becomes aware that it is still positioned in the BSS managed by the access point A 10. The mobile node 1 accesses a wired network by way of the access point A 10, as it did previously.
In a communication denoted by 21 in FIG. 1, the mobile node 1 receives a beacon signal from the access point B 20. Based on the received beacon signal, the mobile node 1 becomes aware that the BSS in which it is positioned has changed. Accordingly, the mobile node 1 conducts a handover due to the change of the BSS, i.e., a handover in a link layer. That is, the mobile node 1 becomes aware that it is now positioned in the BSS managed by the access point B 20, and changes its link layer connection with the access point A 10 to a link layer connection with the access point B 20. Referring to the open systems interconnection (OSI) reference model, since the link layer corresponds to a second layer, the handover in the link layer is called a handover in the second layer or an L2 handover for short. The mobile node 1 accesses a wired network by way of its new access point B 20.
In the communication denoted by 22 in FIG. 1, the mobile node 1 transmits a router solicitation for proxy advertisement (RtSolPr) frame, including information that the BSS in which it is positioned has changed, to the access router A 50 by way of the access point B 20. The access router A 50, which has not received this frame through any other access router, becomes aware that the mobile node 1 is positioned within its subnet.
In the communication denoted by 23 in FIG. 1, the access router A 50 transmits a proxy router advertisement (PrRtAdv) frame, including information that the subnet has not changed, to the mobile node 1 by way of the access point B 20. The mobile node 1 that receives this frame becomes aware that it is still positioned within the subnet managed by the access router A 50. Accordingly, the mobile node 1 does not conduct a handover, i.e., a handover in an Internet Protocol (IP) layer. Referring to the OSI reference model, since the IP layer corresponds to a third layer, a handover in the IP layer is called a handover in the third layer or an L3 handover for short.
In the communication denoted by 24 in FIG. 1, the mobile node 1 receives a beacon signal from the access point B 20. Based on the received beacon signal, the mobile node 1 becomes aware that it is still positioned within the BSS managed by the access point B 20. The mobile node 1 accesses a wired network by way of the access point B 20, as it did previously.
In the communication denoted by 31 in FIG. 1, the mobile node 1 receives a beacon signal from the access point C 30. Based on the received beacon signal, the mobile node 1 becomes aware that the BSS in which it is positioned has changed. Accordingly, the mobile node 1 conducts a handover due to the change of the BSS, i.e., a handover in a link layer. That is, the mobile node 1 becomes aware that it is now positioned in the BSS managed by the access point C 30, and changes the link layer connection with the access point B 20 to a link layer connection with the access point C 30. The mobile node 1 accesses a wired network by way of its new access point C 30.
In the communications denoted by 32 and 232 in FIG. 1, the mobile node 1 transmits an RtSolPr frame, including information that the BSS in which it is positioned has changed, to the access router A 50 by way of the access point C 30 and the access router B 60. The access router A 50 receives this frame by way of the access router B 60, which is a different access router, and thereby becomes aware that the mobile node 1 is not in its subnet.
In the communications denoted by 33 and 233 in FIG. 1, the access router A 50 transmits a PrRtAdv frame, including information that the subnet in which the mobile node 1 is positioned has changed, to the mobile node 1 by way of the access router B 60 and the access point C 30. The mobile node 1 that receives this frame becomes aware that the subnet in which it is positioned has changed. Accordingly, the mobile node 1 conducts a handover due to the change of the subnet, i.e., handover in an Internet Protocol (IP) layer.
In the communication denoted by 34 in FIG. 1, the mobile node 1 receives a beacon signal from the access point C 30. Based on the received beacon signal, the mobile node 1 becomes aware that it is still positioned in the BSS managed by the access point C 30. The mobile node 1 accesses a wired network by way of the access point C 30, as it did previously.
In the communication denoted by 41 in FIG. 1, the mobile node 1 receives a beacon signal from the access point D 40. Based on the received beacon signal, the mobile node 1 becomes aware that the BSS in which it is positioned has changed. Accordingly, the mobile node 1 conducts a handover due to the change of the BSS, i.e., a handover in the link layer. That is, the mobile node 1 becomes aware that it is now positioned within the BSS managed by the access point D 40, and changes the link layer connection with the access point C 30 to a link layer connection with the access point D 40. The mobile node 1 accesses a wired network by way of its new access point D 40.
In the communication denoted by 42 in FIG. 1, the mobile node 1 transmits an RtSolPr frame, including information that the BSS in which it is positioned has changed, to the access router B 60 by way of the access point D 40. The access router B 60, which has not received this frame through any other access router, becomes aware that the mobile node 1 is positioned within its subnet.
In the communication denoted by 43 in FIG. 1, the access router B 60 transmits a PrRtAdv frame, including information that the subnet has not changed, to the mobile node 1 by way of the access point D 40. The mobile node 1 that receives this frame becomes aware that it is positioned within the subnet managed by the access router B 60. Accordingly, the mobile node 1 does not conduct a handover due to the change of the subnet, i.e., a handover in the IP layer.
As described above, the mobile node 1 communicates with an access router to obtain information of a change of a subnet that it accesses, since it does not know whether the subnet has changed. In other words, the mobile node communicates with the access router in order to determine whether to conduct the handover only in the link layer, or to conduct the handovers in both the link layer and the IP layer.
A handover due to movement of a mobile node between homogeneous networks is illustrated in FIG. 1. However, research to support seamless mobility between heterogeneous networks is being conducted.
Especially, wireless technology recently gaining popularity as a main technology is classified into wireless local area networks (WLAN) (the IEEE 802.11 standard) and cellular networks. To support mobility between these wireless networks, organizations participating in wireless standardization, including IEEE 802, 3GPP, 3GPP2, ITU-T and IETF, are actively focusing on solving known problems.
Among these, research on IEEE 802 is the most active, especially IEEE 802.21 WG (Working Group) and IEEE 802.11 WIEN SG (Wireless Interworking with External Networks Study Group).
IEEE 802.21 WG is focused on standardization to provide media independent solutions for mobility between heterogeneous networks. In particular, it has created a new layer 2.5 model between a Media Access Control (MAC) layer and its upper IP layer, thereby making it possible to support efficient mobility in various wired and wireless environments.
In connection with this, the working group of IEEE 802.21 has been conducting discussions about a method of realizing a media independent handover (MIH) protocol. Information about the MIH protocol can be found on the Internet at www.ieee802.org/21.
When a mobile node operating according to the MIH protocol moves to a heterogeneous network, the mobile node can conduct continuous communication since a handover is possible when an access point in the target heterogeneous network supports the MIH protocol.
The above handover in the heterogeneous network may be conducted in the link layer or the IP layer, the same as a handover in a homogeneous network.
A handover in the IP layer moves the mobile node to a new network. In order for the mobile node to receive a new IP address in the new network, the mobile node obtains information about a version of an IP address used in the new network (e.g., Internet Protocol version 4 (IPv4) or Internet Protocol version 6 (IPv6)), and information about a method of allocating an IP address in the new network (e.g., a direct-input allocation method or an auto-allocation method) by communicating with an access point and an access router of the new network.
In the related art described above, when a mobile node moves to a neighboring network, it must temporarily stop providing services while it determines a method of allocating an IP address in the neighboring network in order to receive a new IP address, which may be a problem for mobile communication services supporting seamless communication to a user.